1. Field of the Invention
The invention relates to a die bonder and, more particularly, to a die bonder capable of keeping the substrate smooth during the die-bonding process and increasing the throughput.
2. Related Art
A die-bonding process is one of the important processes in the IC package processes. In the die-bonding process, dies that are cut from a wafer are taken out and bonded onto the substrate for follow-up processes such as wire bonding, molding and the like. With the development of the package technology and the progress of the manufacturing technology, the package structure is getting lighter, thinner, shorter, and smaller. To accommodate this trend, the die is getting larger and thinner. In addition, the substrate that is signal-connected to the die is getting thinner. For example, the currently used substrate may be a super-thin substrate having the thickness equal to or smaller than 0.26 mm.
As shown in FIG. 1, a conventional die bonder 300 includes a paste-dispensing mechanism 301, a die taking/placing mechanism (only a robot arm of which is shown) 302, and a clamping mechanism (only press bars are shown) 304. The paste-dispensing mechanism 301 is used to dispense silver paste 311 onto a substrate 303. The die taking/placing mechanism 302 takes and places dies 312 onto the substrate 303 one by one after the dispensing process of the silver paste 311 is completed. Since the substrate 303 has to be heated to remove the moisture in the substrate 303 before the die-bonding process is performed. However, after the substrate 303 is heated at a high temperature, the substrate may be warped due to the vaporization of the moisture and thermal stresses. To keep the substrate 303 smooth in the paste-dispensing and die-bonding processes, the substrate 303 may be pressed by the clamping mechanism 304 or sucked by a vacuum suction force. However, after the die-bonding process is completed, it is necessary to place the substrate 303 into an oven or use a post-heating method to cure the silver paste 311. At this time, the substrate 303 is usually separated from the clamping mechanism 304 or out of vacuum. This usually warps the substrate 303.
Since the substrate becomes wrapped during the die-bonding process, even though the substrate is smoothened by the clamping mechanism or the vacuum suction force during the paste-dispensing and die-bonding processes, the substrate still tends to return to the wrapped state after the clamping force or the suction force is removed. Therefore, the phenomenon of shrinkage of the silver paste occurs and voids are formed to decrease the reliability of the products.
Furthermore, since the silver paste has to be cured after the die-bonding process is completed, the substrate on which dies are bonded has to be placed into a substrate magazine that is then transferred to the oven for heating. Alternatively, the substrate may be heated directly on the track by way of post-heating to cure the silver paste. However, whether the silver paste is cured by the oven or by the post-heating method, the substrate has to be held up for a period of time according to the operation of the oven or the machine. This results in a time delay and thus decreases the throughput.
Therefore, it is an important subject matter to keep the substrate smooth, to prevent the substrate from being wrapped under the heating process, and to shorten the whole time for the die-bonding process.
In view of the above-mentioned subject matter, it is therefore an object of the invention to provide a die bonder capable of preventing the substrate from being wrapped during the die-bonding process.
Also, another object of the invention is to provide a die bonder capable of speeding up the die-bonding process.
In this invention, a heat-resistant carrier is used to continuously position the substrate so that the substrate can be kept smooth during the whole die-bonding process and warpage of the substrate can be avoided. In addition, the invention also utilizes a circulating conveyor to perform the sequential dispensing process, die-bonding process, and curing process, so as to improve the speed of the die-bonding process and the throughput.
Thus, in order to achieve the above-mentioned objects, the invention provides a die bonder including a conveyor, a pre-heater, at least one carrier, a paste-dispensing mechanism, a die taking/placing mechanism, and a heater. The conveyor continuously operates in a ring-shaped manner. The carrier is carried on the conveyor to position the substrate. The pre-heater heats the substrate. The paste-dispensing mechanism dispenses an adhesive agent onto the substrate. Then, the die taking/placing mechanism places a die onto the substrate at a position where the adhesive agent is dispensed. Finally, the heater is used to cure the adhesive agent so as to bond the die to the substrate.
Since the heat-resistant carrier is used to carry the substrate in the die bonder of the invention and is capable of keeping the substrate smooth, even though the substrate is heated to eliminate the moisture before the die-bonding process, the substrate is not wrapped during the heating process by the vaporization of the moisture and the generation of thermal stresses. Thus, the voids generated due to the shrinkage of the silver paste dispensed on the substrate can be avoided. In addition, the yield of the products is increased. Moreover, the conveyor further conveys the carrier to perform a series of dispensing, die-bonding, and curing processes. During the curing process of the silver paste, since the substrate is positioned on the carrier, the silver paste dispensed on the substrate can be continuously cured. In other words, during the curing process, the substrate does not have to be held up to cure the silver paste. Thus, the curing time is shortened, and the throughput of the products is increased.